One or more embodiments of the disclosure relate to a method of manufacturing a nonvolatile memory device and, more particularly, to a method of manufacturing a nonvolatile memory device, which is capable of improving a retention characteristic by suppressing a charge-sharing phenomenon of a dielectric layer.
In general, nonvolatile memory devices retain data even though the supply of power is stopped. A unit cell of a nonvolatile memory device has a structure in which a tunnel insulating layer, a floating gate, a dielectric layer, and a control gate are sequentially stacked in an active region of a semiconductor substrate. As voltage applied to the control gate from the outside is coupled at the floating gate, the cell can store data. Accordingly, if it is sought to store data within a short period of time and at a low program voltage, the ratio of voltage induced at the floating gate to voltage applied to the control gate must be large. Herein, the ratio of voltage induced at the floating gate to voltage applied to the control gate is called a “coupling ratio.” The coupling ratio can be expressed as the ratio of the capacitance of a gate dielectric interlayer to the sum of capacitances of the tunnel insulating layer and the gate dielectric interlayer.
In the conventional flash memory device, a SiO2/Si3N4/SiO2 (Oxide/Nitride/Oxide, ONO) structure is chiefly used as the dielectric layer for isolating the floating gate and the control gate. From among them, SiO2 typically is deposited using a DCS (dichlorosilane)- or MS (monosilane)-based chemical vapor deposition (CVD) method. The oxide layer formed by this CVD method has a low film quality and a low step coverage characteristic of 85% or less when compared to an oxide layer formed by a typical dry or wet oxidization method. With higher degrees of integration of devices, the thickness of the dielectric layer is reduced to secure the coupling ratio. Thus, the leakage current and a reliability characteristic are deteriorated, and a thickness at both edges of the ONO layer is reduced.
Accordingly, there is a need for a method with an excellent step coverage characteristic. Furthermore, a smile phenomenon occurs due to a bird's beak phenomenon, in which a thickness at both edges of the ONO layer increases due to a subsequent thermal process. In this case, the leakage current increases because an electric field is concentrated on a central portion of the ONO layer, which is relatively thin. Further, there is a problem in that the uniformity of a cell threshold voltage (Vth) distribution deteriorates.